The recent observation of neutrino oscillations with atmospheric and solar
neutrinos, implying that neutrinos are not massless, is a discovery of
paramount importance for particle physics and particle astrophysics. This
invited lecture discusses - hopefully in a way understandable also for the
non-expert - the physics background and the results mainly from the two most
relevant experiments, Super-Kamiokande and SNO. It also addresses the
implications for possible neutrino mass spectra. We restrict the discussion to
three neutrino flavours (nu_e, nu_mu, nu_tau), not mentioning a possible
sterile neutrino.Comment: Contribution to CF 200